Table 3 Methodology for measurements

Hang grip strength

Three trials with a rest of 30 s between the tests will be performed for each hand, with a handheld Takei digital dynamometer and patients will be encouraged to exert their maximal grip strength [1, 56]. An average value will be calculated.

MAMC

This is the midpoint between the lateral edge of the acromion and olecranon process of the radius, on the mid line of the posterior surface of the dominant arm; it is measured with the arm in a supine position, flexed at the elbow with the forearm rotated against the body at 90 degrees, and the hand resting against the torso. Once the midpoint is marked, the arm returns to a supine position with the hand against the thigh. The MAMC is measured around the midpoint mark ensuring the measuring tape is even against the skin (without being taut). This will be repeated twice, and the mean result calculated.

TSF

From the midpoint calculated above, a vertical pinch with a Harpenden calliper, parallel to the long axis of the arm, is made at the landmark in a perpendicular direction. Measurement in millimetres will be taken; it will be repeated twice, and a mean is calculated [57,58,59].

Isokinetic dynamometry

This measures strength and power via knee extension. Maximal muscle strength will be measured as the peak torque [52]. Patients will be seated in an adjustable, straight-backed chair with their hips and their knees flexed at 90°; their pelvis and the thighs will be secured by a broad strap with their arms crossed in front of their chest. After the instruction and 2-3 practical trials, the patient will be asked to extend, then flex the leg with maximal effort, for 5 repetitions. Both legs will be tested, unless contraindicated by pain or other symptoms. Unilateral limb tests will be performed on the non-biopsied leg, following a muscle biopsy [60, 61].

US scan

Patients will lie in a semi-supine position with legs resting flat on a bed. All images will be taken at 50 % of femur length (measured from the greater trochanter to the lateral knee joint space). The maximal anatomical ACSA of human quadriceps is shown to be at ~50% of the femur length [62].

Two-dimensional B-mode ultrasonography Esoate MyLab Alpha point of care ultrasound, 4.6 cm probe (SL1543, 13-4Mhz scanning frequency)) will be performed.

Three longitudinal scans will be taken at 50% femur length of the vastus lateralis muscle with the probe aligned to the fascicles; allowing for quantification of fascicle length and pennation angle. Vastus lateralis muscle thickness (defined as the perpendicular distance between the superficial and deeper aponeurosis) will be obtained. All variables will be obtained offline via image J imaging software and will be presented as a mean.

For assessment of all quadricep muscles, two extended field of view ultrasound images will be taken at 50% femur length; this will allow for the quantification of quadriceps ACSA. Echogenicity can be determined using a computer-assisted grey-scale analysis offered by ImageJ [63, 64].

MRI femur

Axial and sagittal plane scans of each thigh will be obtained using an MR 3T scanner for higher quality, efficient imaging capture and 3D reconstruction. A T1 weighted Spin Echo protocol will be used (repetition time 600ms, echo time 15.2 ms, Field of view 512 × 512 mm, slice thickness 10mm, no gap between slices).

Patients will lie supine on a preparation bed for up to 20 min to allow fluid shift stabilisation. A series of axial plane scans along the entire length of the quadriceps muscle group and sections at the L3 lumbar spine (L3 lumbar spine to quadriceps insertion on the tibia) will be collected.

The contours of the quadriceps will be digitalised offline using the Osirix DICOM image analysis software (Pixmeo, Geneva, Switzerland) and the quadriceps muscle volume will be calculated [65]. 3-dimensional acquisition of both thighs and a Dixon sequence will be performed for fat analysis.

Quadriceps muscle ACSA will be measured as described in the above. This midpoint of each femur length and the midpoint of VL (which is where ultrasound CSA measurements are taken from) will be marked with an external marker to ensure this is identified on MR images for analysis purposes and comparisons with ultrasound measurements. All image results will undergo a review by Consultant Musculoskeletal Radiologist.

Muscle biopsy

The patient will be fasted for ~6 h prior to the procedure. The ultrasound performed will identify the correct position to ensuring the sample is taken from the muscle belly. The non-dominant limb will be used if the dominant limb is not feasible.

A small area of skin overlying the outer thigh will be cleaned with iodine solution. 5–10ml of 1% lignocaine is infiltrated into the subcutaneous adipose tissue and down to the muscle. After adequate anaesthetic, a small incision is made in the skin (approximately 5–7mm in length). A needle is inserted into the muscle and a small amount of muscle is taken using a well-described technique with a Bergstrom needle. A few passes may be performed. The incision will be closed using ‘steri-strips’ and a single suture, if required. A small dressing will then be placed over the biopsy site. Pressure and an ice compress will be applied to the area for 10 min by hand. A pressure bandage which will stay on for 8 h to decrease the risk of bruise formation. Patients will be asked to keep this area dry for at 3–5 days. All patients will receive after care advice and contact if any problems do arise.